This invention relates to electrosurgical devices and in particular to such devices having sesquipolar electrode structures incorporated therein.
In conventional monopolar electrosurgery, radio frequency (RF) power of various wave forms and amplitudes is applied to the body of a patient with a very small area active electrode such that a localized interaction produces cutting, coagulation, fulguration, or desiccation. The return path for the RF current is via a large area return electrode so that interaction at this interface is insignificant.
In conventional bipolar electrosurgery, a pair of electrodes are close together, small and essentially identical so that significant and equal interactions occur with the body at both surfaces. When attempting to make electrosurgery more simple and more safe, one is drawn to the bipolar mode. No lasting electrical connections are made to the patient, it is all in the hand of the surgeon. Further, bipolar devices, especially when used with RF sources that are isolated from ground, significantly reduce the danger of RF burns at intentional and at inadvertent ground connections to the patient. Also, possible dangers from passage of large RF currents through the body are eliminated, and the interaction of the RF with other instrumentation is minimized. The convenience and added safety of not having a large, separately placed return electrode are also significant.
A number of bipolar devices have been proposed and produced. The most commonly used bipolar electrode devices appear to be the tips of forceps (current passes from tip to tip through the grasped flesh), and dual needles. For many years, minor coagulation and desiccation, especially in cosmetic and neurosurgery have been performed in the bipolar mode. However, bipolar technology has not proved to be a satisfactory substitute for conventional monopolar electrosurgery in most applications, especially those requiring cutting and heavy coagulation. The most fundamental difficulty is that biactive electrodes require an equal voltage drop at each of the electrodes. When arcing is required as for cutting or heavy coagulation, this taxes the output capability of the available generators. Modification of the generator to produce such high voltages results in a problem of extraneous arcs at the electrodes. However, a more important problem is that, when sufficient voltage for correct bipolar arcing operation is present, conditions for starting to cut are too violent for any but the most crude surgical techniques. If one electrode touches the flesh before the other when starting to cut, the initial arc at the second electrode is unduly destructive. Thus, there are obvious safety and convenience advantages associated with bipolar devices, and yet there is a lack of available equipment for obtaining these advantages for most applications such as cutting or heavy coagulation.
For the purposes of the present invention, "sesquipolar" (sesqui from the Latin for 11/2 times) electrode devices are utilized. In such devices, the area of the return electrode is substantially smaller than that of monopolar devices. The term "sesquipolar" has been defined for purposes of this invention and the definition thereof will be further elaborated hereinafter. The active and return electrodes of a sesquipolar device may both be in the operational site, as with bipolar devices, but only one of them is intentionally highly interactive. Because the return electrode is rather small, there is some interaction, making it intermediate between conventional mono and bipolar modes of electrosurgery.
The sesquipolar return electrode is not merely a scaled down return electrode of the more conventional monopolar technology. Any decrease in the size of the conventional monopolar return electrode (even though an order of magnitude away from the sesquipolar device of this invention is rejected by the safety committees and standards groups). Indeed, in monopolar electrosurgery the avoidance of any detectable interaction at the return electrode (which is allowable in the sesquipolar mode) is fundamental. Otherwise burns obtained at nonsurgical sites can result in disfiguration and concomitant suffering. In fact, burns are occasionally obtained at small area inadvertent connections to ground, and at improperly administered return electrodes. Sesquipolar technology, in contrast, may be viewed as bipolar from the safety point of view, and return electrode area will not be a matter of concern from a safety point of view. And yet, there are very clear-cut distinctions from conventional bipolar systems. For example, bipolar technology has carefully respected symmetry, insisting categorically that both electrodes be equally active.
Sesquipolar devices provide the advantages of both the bipolar and the monopolar devices, while larlely eliminating the technical difficulties of the bipolar and the dangers associated with conventional monopolar electrosurgical devices. For example, since the less active electrode of sesquipolar devices operates with significantly reduced voltage drop, the output of conventional electrosurgical generators is sufficient to drive this type of electrode system in major operations. There is no problem of control in delicate surgery.
There has been disclosed in U.S. Pat. Nos. 2,004,559; 2,002,594; and 2,056,377 electrosurgical tools wherein the ratio of the area of the active electrode to the return electrode may be small although there is no explicit teaching of this in the above patents. Further, the active and return electrodes in the above patents are relatively pivotally mounted with respect to one another and thus the electrosurgical tools described therein are essentially limited to the cutting of flat surfaces and thus unduly limited for general surgical purposes.